This invention relates to neurosurgical apparatus generally, and more particularly, to stereotactic systems for use in neurosurgery.
During the 1970""s radiological imaging systems were developed to assist surgeons in ascertaining the internal condition of a patient in greater detail. Specifically, computer assisted tomography (CAT) systems were developed to enhance images generated from data produced during a radiological scan of a patient. The patient is placed within a gantry, and a radiation source and radiation detectors are positioned opposite one another to be rotated about a portion of the patient""s body. The data generated by the radiation detectors are utilized by a computer to generate radiographic images or xe2x80x9cslicesxe2x80x9d of the body position to give a doctor greatly enhanced views through the area of interest.
Later radiographic imaging systems included magnetic resonance (MRI) and positron emission tomography (PET) imaging which generate images from energy sources that do not use x-rays or the like. These devices are useful because they provide different or additional information about organs or tissues than CAT scan images. In this application the term scanners refers to imaging devices regardless of the technique utilized to generate the images.
Neurosurgery may be performed to investigate, repair, or remove anomalies located within the brain of a patient. The environment of such surgeries is challenging in that the organ of interest, the brain, is surrounded by relatively thick bony structure, the skull. The only presurgery access to the brain available to a surgeon is through images generated by an imaging system.
Because of the inaccessibility, size, and roughly hemispherical shape of the brain, specifying the locus of a point inside the brain generally requires reference to some fixed external reference system. To provide a surgeon with sufficient information to locate an area of interest on an image, such as a tumor or lesion, a variety of systems have been developed to provide a reference point or points which may be used to match the patient""s anatomical structure with the structures displayed in the images. These systems typically require that a frame be rigidly fixed to a patient""s head to provide a reference point or points. Once the reference structure is attached to the patient, the image data is generated with the reference frame fixed in relation to the imaging device. That is, there is typically a mechanical coupling between the reference structure and the imaging device. After the data is collected, the patient may be removed from the scanner but the reference frame must remain attached to the patient""s head. The reference frame remains attached throughout surgery so the surgeon can correlate image information about patient anatomical structures to a position within the patient""s skull located with reference to the frame.
While such systems provide surgeons with a remarkable ability to locate areas of interest within a patient""s brain based upon the data acquired by radiological scanners, the required reference frames are cumbersome and complicate the acquisition of radiological data. To preserve the location of the reference frame, it must remain attached to the patient""s head throughout the scanning procedure and the surgical procedure. Because the reference frames may weigh several pounds and must be securely fastened to the head, they can be uncomfortable to the patient. The distances the frames extend from the patient""s head also present difficulties in maneuvering the patient. Additionally, patients with larger than normal heads often cannot be fitted with stereotactic frames.
In an effort to reduce the awkwardness of the reference structure and the discomfort it causes a patient, a stereotactic system using a skull ring which may be mounted to a patient""s skull was developed. The ring is a relatively small metallic circle that is attached to a patient""s head using cancellous screws. Once the ring is in place, a transfer plate having two openings, one of which has a rotatable ball and socket mechanism mounted therein, is secured within the ring. The transfer plate is also provided with a radiological opaque marker which may be discerned in the radiological images generated by the scanner. The patient is then placed inside a scanner and a member extending from the ball and socket is coupled to the machine. Once the patient has been oriented within the scanner for the collection of image data, the ball and socket is locked in a fixed orientation.
Following the collection of image data, the member extending from the ring and patient which was coupled to the scanner is disconnected so the patient may be removed. The ball and socket remains locked in its orientation so the orientation of the transfer ring on the patient""s skull may be later duplicated for locating a target.
After removing the transfer plate holding the ball and socket from the skull ring attached to the patient""s head, the plate is attached to a member extending above a frame table to duplicate its position and orientation on the patient""s head. The images generated by the scanner are viewed and the coordinate data of a selected target, such as a lesion or tumor, and the radiological marker of the transfer plate are determined. Using this coordinate data and the indicia marked on the frame table, a target marker is maneuvered on the frame table so it identifies the target position with respect to the radiological marker. A second ball and socket mechanism is placed in the second opening of the transfer plate. Thereafter, an instrument such as a biopsy probe may then be extended through the second ball and socket to the target point to define a distance and path to the target. The second ball and socket is then locked into place to preserve the orientation to the target and the distance to the target is marked on the probe.
The transfer plate bearing the second ball and socket mechanism may then be removed from the member above the frame table and reattached to the skull ring on the patient""s skull with the second locked ball and socket defining a path to the selected target. Thereafter, a biopsy probe may be used to mark the patient""s skull and a craniotomy performed at that point to provide an opening in the patient""s skull. The biopsy probe may then be extended through the opening in the second ball and socket to the depth marked on the probe to place the biopsy probe within the lesion or tumor. In this manner, the surgeon is able to accurately place the biopsy probe without unnecessary searching to locate the tumor or lesion prior to performing the biopsy. A further description of the above technique and apparatus is given in U.S. Pat. Nos. 4,805,615 and 4,955,891 to which reference may be had.
The above-described manner for performing the biopsy facilitates the collection of image data in a number of ways. First, the reference structure attached to the patient""s skull is small in comparison to the reference frames previously used. Second, the removable plate with the ball and socket openings permit accurate location of a target area within a patient""s brain prior to performing a craniotomy. Third, the removable plate with the bail and socket mechanisms ensures correct placement of the plate on the patient""s skull and preserves the accuracy of the path to the target identified on the frame table. While this method greatly facilitates locating the target area within a brain, it fails to provide the surgeon with information regarding the intervening tissue area between the craniotomy opening in the skull and the target area, which lies within and possibly deeply within the brain. Furthermore, the image data generated by a scanner is not necessarily oriented transversely to the location of the opening of the ball and socket of the reference ring and thus does not provide image data at various depths between the craniotomy opening and the target area to assist the surgeon in evaluating the path to the target. Thus, while the surgeon need not search to locate the target, the surgeon does need to carefully retract the brain tissue along the path to reach the target. Otherwise, damage to any sensitive areas that may lie along the pathway is possible. The reference systems discussed above do not assist a surgeon in identifying the exact location of any such sensitive areas prior to performing the craniotomy and traversing the path to the target.
In addition to identifying the locus of the lesion or injury within the brain it is often critical to determine a suitable pathway through the brain to access that locus, in order to minimize damage to the intervening tissue. Thus, identifying the pathway to the site may be almost as critical as identifying the site itself. The above-described system has been inadequate in this respect.
In an effort to provide more automatic matching between image data and the patient as placed in surgery, systems have been developed that perform xe2x80x9ccoregistrationxe2x80x9d. Coregistration is a process by which a computer matches fiducials associated with image data to fiducials associated with the patient""s body. The image fiducials are typically selected by using a mouse and cursor to identify on a displayed image points that lie on a patient""s skin. An articulated arm and probe are coupled to the computer to provide coordinate data for points external to the computer. Using the arm and probe, the user selects points on the patient that correspond to the selected image fiducials and the computer executes a program that matches the corresponding points. After a sufficient number of points have been selected (usually at least 8), the computer may identify the point in the displayed images that corresponds to the position of the probe proximate the patient""s head. Such a system is made by Radionics of Brookline, Massachusetts and is identified by its product name The Operating Arm.
Such a system provides xe2x80x9cnavigationalxe2x80x9d information to a surgeon, that is, the surgeon may bring the probe to a particular location on or within a patient""s head and have that location identified on the displayed image. In this way, the surgeon may view areas on the displayed image and determine their proximity to the probe location. In that manner, the surgeon may confirm the surgical approach to a target.
While these systems provide confirming navigational information they still do not project a stabilized image of the surgical path on a displayed radiological image prior to a craniotomy being performed. Such systems cannot project a stabilized path because the surgeon cannot consistently orient and stabilize the probe at exactly the same position each time the path needs to be viewed. As a consequence, such systems do not identify or persistently indicate a path to a target because the probe is operated by hand. Moreover, such systems do not ensure that the surgeon is following any path the surgeon may have selected as a result of viewing the displayed radiological images.
What is needed is a system that permits a surgeon to select, evaluate, and lock into position a path to a selected target prior to performing a craniotomy. What is needed is a system that guides a surgeon along the evaluated surgical path to a target during and after the craniotomy. What is needed is a way to select and preserve a plurality of selected paths to multiple targets after the paths have been evaluated.
These and other problems of previously known systems are overcome by a system in accordance with the principles of the present invention. This system includes an imaging display system for displaying radiological images, an image fiducial selector coupled to the imaging system for selecting fiducials on an image displayed on the display system, a target selector coupled to the imaging system for selecting a target on an image displayed on the display system, an articulated arm and probe coupled to the imaging system, which provides spatial coordinates for the probe with reference to the imaging system so that a position associated with the probe is displayed on the displayed image. A patient fiducial selector is coupled to the imaging system and to the articulated arm for selecting fiducials on a patient that correspond to the fiducials selected for the displayed image. A coregistration processor coregisters the patient fiducials to the selected image fiducials so that the coordinates provided by the articulated arm may be matched to the displayed image whereby a position of the probe may be displayed on the displayed image. A probe holder holds the probe of the articulated arm in proximity to a patient""s head. the holder being selectively lockable to maintain a position proximate the patient""s head. By using this system, a surgeon may evaluate the path displayed on said displayed image between said probe position and said selected target.
A system in accordance with the principles of the present invention permits a patient to be scanned without any plate or frame reference being affixed to the patient. The system coregisters image fiducials with selected anatomical features of a patient so the position of the probe may be displayed on a radiological image and a path to a selected target projected on the image. A surgeon may evaluate the path to the selected target and lock the probe position in place if the path is deemed acceptable. The surgeon may then mark the appropriate spot on the patient""s head for the craniotomy. In a similar manner, the paths to other targets may be identified and marked prior to any craniotomy.
The system may further include surgical instrument collars adapted to fit within the probe holder so an instrument may be inserted through the collar in the correct orientation and position to follow the evaluated path to the selected target. Thus, the probe holder may be used to facilitate a surgeon""s path selection and evaluation and then preserve that path as well as guide instruments along that path.
The system of the present invention may further include an arc carrier rod for defining a predetermined radius to a selected target. A grooved arc may be rotatably mounted to the reference rod, and the probe holder mounted in a probe adapted to slide within the grooved arc. Thus, the grooved arc may be rotated in a hemispheric fashion about the patient""s head and the probe plate and holder slid along the grooved arc to define numerous entry points for evaluation by the surgeon using the radiological display system. The imaging system is further provided with a processor for interpolating data from the radiological data generated by the scanner to provide a view along the probe from any entry port selected along the hemispheric stereotactic system positioning as long as the probe reaches the holder. Utilizing this system, a surgeon may evaluate a number of entry points and select the one which presents the least risk to the patient.
Another advantage of the present system is that after a target has been selected and the biopsy or surgical procedure performed on the target, the surgeon may select a second target of interest within the patient""s brain. After this selection, the probe holder may be unlocked and the probe reinserted to define a second path to the second selected target. The hemispheric stereotactic system may then be attached to provide multiple entry points to the second target for evaluation and, once a suitable path is selected, a procedure may be performed on the second target. Utilizing the system in this manner facilitates a surgery wherein radioactive seeds are implanted in various areas of a tumor with the effect that the radiation is primarily limited to the area of the tumor. This type of use also assists a surgeon in the precise placement of multiple depth electrodes in a patient""s brain for monitoring.